Alzheimer's disease (AD) is a neurodegenerative disease that affects over 4 million Americans. We are the first to demonstrate that brain blood vessels release neurotoxic proteins in Alzheimer's disease. However, the factors that cause this vessel dysfunction are not known. It is our hypothesis that risk factors involved in the pathogenesis of atherosclerosis are also causally linked to the development of vascular-mediated neuronal cell death in Alzheimer's disease. Our studies are timely and important as increasing evidence points to a link between atherosclerosis and Alzheimer's disease. Aim 1: To determine the effects of systemic oxidant stress or hyperlipidemia on vascular thrombin release, vascular-mediated neurotoxicity and on the cognitive performance of apoE transgenic mice. Brain blood vessels isolated from apoE knockout or transgenic mice expressing human E3 or E4 are used to assess the role of apoE isoforms on vascular expression of thrombin. Diet-induced hyperhomocystinemia and hyperlipidemia, are used to assess the role of oxidant stress and lipids, respectively, on vascular thrombin release and vascular-mediated neurotoxicity. Also, these transgenic mice are utilized to evaluate possible apoE isoform-specific effects of oxidant and lipid stress on impairments in learning and memory. Aim 2: To determine if risk factors involved in the pathogenesis of atherosclerosis are also causally linked to the development of vascular-mediated neuronal cell death in Alzheimer's disease. Brain microvessels are isolated from AD patients and non-demented patients and analyzed for levels and/or activity of thrombin and other possible neurotoxic proteins, including, matrix metalloproteinases (MMPs), inflammatory cytokines and chemokines, and endothelin-l. Protein levels are determined by ELISA and Western blots and Mrna levels assessed by Northern blots and RT-PCR. The role that apoE isoforms play in regulating these proteins is determined by comparing microvessels isolated from patients with different APOE genotypes. In vitro addition of oxygen species or lipid molecules to isolated brain microvessels is used to assess the effects of oxidative stress and lipids, respectively, on release of thrombin, MMPs, inflammatory proteins, and endothelin-l. Apoptosis and necrosis are measured in cultured neuronal cells exposed to these proteins. These results would, for the first time, identify a mechanistic cascade linking cardiovascular risk factors to vascular-mediated neuronal cell death in Alzheimer's disease and identify novel targets for therapeutic intervention.